Internally Non-LTI Systems Based on Delays, With Application to Companding Signal Processors

We convert linear continuous-time systems based on delays to internally nonlinear ones, with unchanged input–output behavior. The internal nonlinearities can be chosen so that the internal modified noise transfer functions result in improved output signal-to-noise ratio for small inputs, thus extending the usable dynamic range. This results in companding signal processors, of which two examples are given—one using syllabic and one using instantaneous companding. This study complements earlier work on externally linear continuous-time systems with rational transfer functions and on such systems containing discrete-time delays.